The evapotranspiration process in green roofs: A review

Previous research has shown that most of the green roof benefits are related to the cooling effect. In the literatureavailable, however, it is still not clear how and how much the evapotranspiration affects the performance of agreen roof. In order to fill the gap in this research topic, this study carries out a review on the cooling effect dueto the evapotranspiration process of green roofs. First of all, an overview of the evapotranspiration phenomenonin green roofs, as well as the equipment and methods used for its measurement are presented. Then, the mainexperimental results available in literature, the physical-mathematical models and the dynamic simulationsoftware used for the evaluation of the latent heat flux are also analysed and discussed among the availableliterature. Moreover, this review proposes a classification of the results carried out by previous studies asfunction of the main parameters affecting the evapotranspiration process (e.g. volumetric water content, stomatal resistance, Leaf Area Index, solar radiation, wind velocity, relative humidity, soil thickness, and substratecomposition). Additionally, a sensitivity analysis of the results obtained from the literature allowed underliningthe correlation among the main factors affecting the evapotranspiration. Finally, a vision of the world areawhere green roof studies were performed is provided. From the results, it is possible to emphasize that most ofthe studies that evaluated the evapotranspiration used high precision load cells. Furthermore, all the heattransfer models of green roofs considered in this review took into account the latent heat flux due to evaporationof water from the substrate and plants transpiration, however, only few of them were experimentally validated.